Diphosgene → N-[(5S)-3-cyano-9,10,11-trimethoxy-6,7-dihydro-5H-dibenzo[a,c]cyclohepten-5-yl]acetamide

Trichloromethyl chloroformate (0.094 ml; 0.77 mmol) was added in portions at 0° C. to a solution of N-[(5S)-3-carbamoyl-9,10,11-trimethoxy-6,7-dihydro-5H-dibenzo[a,c]cyclohepten-5-yl]acetamide (0.2 g; 0.484 mmol), (prepared as described for Example 29) and trimethyl phosphate (0.306 ml; 2.6 mmol). The mixture was allowed to warm up and then heated at 60° C. for 5 minutes. The reaction mixture was poured onto ice and stirred. The resulting precipitate was filtered, dried and purified by flash chromatography, eluting with dichloromethane/ethyl acetate (1/1) to give N-[(5S)-3-cyano-9,10,11-trimethoxy-6,7-dihydro-5H-dibenzo[a,c]cyclohepten-5-yl]acetamide.